1. Field Of The Invention
The present invention relates to a reflective liquid crystal display device which realizes a bright display.
2. Description Of The Related Art
A liquid crystal display device is a non-light-emitting device which conducts a display by modulating light ambient and incident upon the device. Therefore, power consumption in a liquid crystal display device is low. Moreover, it is thin and lightweight. Having such excellent characteristics, it has been widely used in information display apparatuses such as watches, calculators, computer terminals, word processors, TVs and the like.
In recent years, as represented by the coined phrase "advanced information society", an ever-increasing amount of information has been distributed and circulated. Accordingly, there has been an increasing demand by individuals for personal collection and selection of information. Under such a circumstance, there has been a widely recognized need for a portable information apparatus for personal use such as a PDA. Such an apparatus has been longed for and is now positively developed.
In such a portable information apparatus, an information display device as a man-machine interface plays an important role and is considered the key device for the apparatus. Such a display device of the portable information apparatus is required to be thin, light weight, capable of displaying a great volume of information, superior in visibility, and low in power consumption. A liquid crystal display device has been developed which is expected to meet these requirements.
Particularly, a reflective liquid crystal display device can be a suitable display device since it efficiently uses ambient light, thereby sufficiently exhibiting a low power consumption characteristic which is inherent in liquid crystal display devices.
However, when TN or STN mode, the currently preferred display modes, is employed in a reflective liquid crystal display device which incorporates no backlight, two polarizers are required to be provided in the device; hereby resulting in a dark display. Therefore, the TN or STN mode can be employed only in a black and white reflective liquid crystal display device, but it has not been employed in a color reflective liquid crystal display device, since a color reflective liquid crystal display device has to be necessarily provided with a color filter as well as the polarizers and, therefore, a practical brightness cannot be achieved.
Thus, conventionally, a guest-host mode (also referred to as the "GH mode", hereinafter) has been mainly employed in the color reflective liquid crystal display device. In this display mode, a dichroic dye is dissolved in a liquid crystal material as a solvent, and a display is conducted utilizing the anisotropy of the absorption coefficient of the dichroic dye. Thus, a color display can be realized, without any polarizer or color filter, by controlling the orientation of the liquid crystal molecules with an applied electric field and thereby simultaneously changing the orientation of the dye molecules.
For a conventional reflective GH display device, improvement of display characteristics such as contrast and brightness of the display has been discussed while simplifying the manner the liquid crystal molecules are oriented in the presence or absence of an applied voltage. However, the improvement of the characteristics may not have been adequately discussed based on the conventional theory since, in practice, the orientation of the liquid crystal molecules changes in a more complicated manner as a voltage is applied in an actual liquid crystal display device.